2020 Volume 45 Issue 279 Pages 1-9
A long-term operation methodology is proposed for hybrid ground source heat pump (GSHP) systems combined with cooling towers. In this methodology, the calculation conditions, which are the apparent effective thermal conductivity of the ground, cooling/heating load of the GSHP system, and the heat pump COP, are modified by using measurement data. Then, the long-term temperature variation in the ground surrounding the ground heat exchangers (GHEs) is predicted through a simulation, and the optimum control parameter (Set temperature of the cooling tower operation) is determined. The proposed methodology was applied to a hybrid GSHP system installed in an office building. From the results, it was concluded that the operation without the cooling tower operation was optimal. This was because the estimated apparent effective thermal conductivity of 4.5 W/(m・K) was large and the maximum cooling load was smaller than that predicted in the design phase. The result of monitoring for 8 years showed that although the total heat injection rate of GHEs was approximately five times the total heat extraction rate, the long-term increase in the inlet temperature of the primary side of the heat pump was 1-2℃ and the inlet temperature was less than 30℃. In addition, the long-term variation in the measured inlet temperature was similar to that of the inlet temperature calculated by the simulation. Therefore, it was confirmed that the proposed methodology was effective.
